Every 5 years or so I have to make a dozen circular shear blades. The
finished blades are 8" x 1" with a 4" bore. I get sawn disks that are a
bit over. The last time I did this I made a trepanning bit for the
bores then finished the bore with a boring bar. I do have a 10 hp Reed
Prentice lathe that does the job well without complaining. It's a nice
bonus top have a dozen of the cut-outs to make small parts and dies!

The problem is that I can't find the trepanning tool I made and know
almost nothing about commercial ones. I remember what a bitch it was
making the last one and I really don't want to make another. When I did
this job last, I could only cut half way through the 1" and had to flip
the blank. I also broke or chipped the business end often and frankly
the damn thing kind of scared me.

Where and what commercial tool should I get? What's the correct
technique to do this?